O'Neil Shawn T, Bump Joseph K, Beyer Dean E
School of Forest Resources and Environmental Science Michigan Technological University Houghton MI USA.
Present address: U.S. Geological Survey Western Ecological Research Center 800 Business Park Dr. Suite D Dixon CA, 95620.
Ecol Evol. 2017 Oct 28;7(22):9518-9530. doi: 10.1002/ece3.3463. eCollection 2017 Nov.
Understanding landscape patterns in mortality risk is crucial for promoting recovery of threatened and endangered species. Humans affect mortality risk in large carnivores such as wolves (), but spatiotemporally varying density dependence can significantly influence the landscape of survival. This potentially occurs when density varies spatially and risk is unevenly distributed. We quantified spatiotemporal sources of variation in survival rates of gray wolves () during a 21-year period of population recovery in the Upper Peninsula of Michigan, USA. We focused on mapping risk across time using Cox Proportional Hazards (CPH) models with time-dependent covariates, thus exploring a shifting mosaic of survival. Extended CPH models and time-dependent covariates revealed influences of seasonality, density dependence and experience, as well as individual-level factors and landscape predictors of risk. We used results to predict the shifting landscape of risk at the beginning, middle, and end of the wolf recovery time series. Survival rates varied spatially and declined over time. Long-term change was density-dependent, with landscape predictors such as agricultural land cover and edge densities contributing negatively to survival. Survival also varied seasonally and depended on individual experience, sex, and resident versus transient status. The shifting landscape of survival suggested that increasing density contributed to greater potential for human conflict and wolf mortality risk. Long-term spatial variation in key population vital rates is largely unquantified in many threatened, endangered, and recovering species. Variation in risk may indicate potential for source-sink population dynamics, especially where individuals preemptively occupy suitable territories, which forces new individuals into riskier habitat types as density increases. We encourage managers to explore relationships between adult survival and localized changes in population density. Density-dependent risk maps can identify increasing conflict areas or potential habitat sinks which may persist due to high recruitment in adjacent habitats.
了解死亡率风险中的景观格局对于促进受威胁和濒危物种的恢复至关重要。人类会影响大型食肉动物如狼()的死亡率风险,但时空变化的密度依赖性会显著影响生存景观。当密度在空间上变化且风险分布不均时,这种情况可能会发生。我们在美国密歇根州上半岛种群恢复的21年期间,对灰狼()存活率的时空变化来源进行了量化。我们专注于使用带有时间依存协变量的Cox比例风险(CPH)模型来绘制随时间变化的风险图,从而探索不断变化的生存镶嵌图。扩展的CPH模型和时间依存协变量揭示了季节性、密度依赖性和经验的影响,以及个体水平因素和风险的景观预测因子。我们利用结果预测了狼恢复时间序列开始、中间和结束时不断变化的风险景观。存活率在空间上有所不同且随时间下降。长期变化是密度依赖性的,诸如农业用地覆盖和边缘密度等景观预测因子对生存产生负面影响。生存也随季节变化,并且取决于个体经验、性别以及常住与暂居状态。不断变化的生存景观表明,密度增加导致人类冲突和狼死亡率风险的可能性更大。在许多受威胁、濒危和正在恢复的物种中,关键种群生命率的长期空间变化在很大程度上未得到量化。风险变化可能表明源 - 汇种群动态的潜力,特别是在个体抢先占据合适领地的地方,这会随着密度增加迫使新个体进入风险更高的栖息地类型。我们鼓励管理者探索成年个体生存与种群密度局部变化之间的关系。密度依赖性风险图可以识别出冲突不断增加的区域或潜在的栖息地汇,由于相邻栖息地的高繁殖率,这些区域可能会持续存在。